In picture readout devices such as scanners, fax machines, multi-function printers and copiers, a linear light source is required to illuminate an object in the background of liquid crystal. One method is making use of a linear light source and combining a light guide bar to convert the linear light source into a planar light source, thereby providing backlight for a liquid crystal panel.
FIG. 1 shows a linear light source used in picture readout devices and liquid crystal modules in U.S. Pub. application Ser. No. 10/288,444, wherein a convex polygonal light guide bar and a linear light source having a reflecting plane is disclosed. The linear light source 10′ includes a light guide bar 20′ and a light source component 30′. The light guide bar 20′ is a convex polygonal cylinder, and includes an incident plane 220′, an emission plane 240′, a reflecting plane 230′ and a plurality of reflecting layers 250′. Light of at least an LED of the light source component 30′ first passes through the incident plane 220′, is reflected in the reflecting layers 250′ of the convex polygonal cylinder to the reflecting plane 230′, and then is projected out via the emission plane 240′.
FIGS. 2A and 2B show showing surface processing of the reflecting plane disclosed in U.S. Pub. application Ser. No. 10/288,444. The inner surface of the reflecting plane is processed. There are two ways of processing the surface texture. One way is processing in sections to let each section have a different roughness for increasing/decreasing the reflection, refraction, and absorption coefficients. The surface with a high roughness has a large scattering capability and a large reflecting angle. On the contrary, the surface with a low roughness has a small scattering capability and a small reflecting angle, and whose light flux can be changed simultaneously. The other way is let the surface far away from the light source have a higher roughness and the surface near the light source have a low roughness.
Accordingly, the above disclosure mainly processes the surface of the reflecting plane to obtain a uniform light. However, how to enhance the uniformity and brightness of the emission light is still an important topic for research.